1. Field of the Invention
The present invention relates generally to scheduling transmissions in communication systems.
2. Description of Related Art
New technical challenges emerge as telecommunication systems evolve from a second generation system offering pure voice services to a third generation system providing mixed voice and data services. In meeting data service demands, new performance metrics and algorithms need to be defined in order to optimize data performance.
The CDMA 3G-1× Evolution Data Only system (1×-EV-DO, also known as a High Rate Packet Data (HRPD) system) is an evolution system of cdma2000 3G-1× system, and is a pure data system to provide data services to mobile users. In 1×-EV-DO, a scheduler or scheduling function is provided in a base station controller in order to provide fast scheduling or management of system resources based on channel quality feedback from one or more mobiles. In general, a scheduler selects a mobile for transmission at a given time instant, and adaptive modulation and coding allows selection of the appropriate transport format (modulation and coding) for the current channel conditions seen by the mobile.
In second generation wireless communications systems such as those of the IS-95 standard, applications typically employ voice-based communication schemes, in which a connection between the base station and the mobile is a dedicated connection. Since these are essentially fixed connections, there is no need for prioritizing the order of transmission to the active users served by the system (an active user is a user with data to transmit at a current time instant). However, with the emergence of third generation wireless data communications systems, such as CDMA-2000 standard systems and 1×-EV-DO, management of system resources is paramount. This is because properties of data differ significantly from properties of voice. For example, a data transmission, unlike a voice transmission, is not necessarily continuous and may be embodied as a burst transmission or an intermittent-type transmission between a base station and a mobile, for example. Accordingly, a base station in a third-generation system will attempt to manage a large pool of data users by assigning radio resources to each user for transmission. Typically this is done utilizing a prioritization scheme controlled by a scheduler in the base station controller. In a conventional prioritization scheme, idle mobile's are assigned a lower priority than mobile with data to transmit.
Accordingly, the scheduler must be able to manage these large numbers of users without wasting radio resources of the communication system. This management function becomes even more important as a base station attempts to meet QoS (Quality of Service) requirements. QoS is a general term that may represent a number of different requirements. As a basic tenant, QoS is indicative of providing guaranteed performance (e.g., such as a minimum/maximum data throughput, a minimum delay requirement, a packet loss rate, and a packet download time, etc.) in a wireless communication system.
Quality of Service (QoS) differentiation in wireless data networks allows network operators to generate more revenue than is possible with best-effort scheduling policies. The promise of additional revenue is based on the willingness of end users (subscribers) to pay more for perceptible improvements in service (e.g., lower latency, higher throughput, or more predictable performance). QoS differentiation also enables deployment of new services (e.g., streaming audio/video, packet voice etc.) that cannot be provided with acceptable quality over best-effort scheduling policies or algorithms such as highest rate user first (HRUF)) scheduling, maximum carrier to interference ratio scheduling (Max C/I) and proportional fair (PF) scheduling, etc.
There has been efforts to develop scheduling algorithms for the scheduler in the base station controller to achieve QoS guarantees in wired and wireless networks. Prior efforts have resulted in scheduling techniques such as pure peak picking scheduling (i.e., the aforementioned HRUF or Max C/I)) proportional fair (PF) scheduling and variations of PF scheduling, referred to as Proportional Fair with Minimum Rate (PFMR) scheduling and Maximum Throughput with Minimum Rate (MTMR) scheduling, for example. However, because of the differences in channel characteristics, many of the QoS approaches designed for wired-line networks are not directly applicable to wireless data airlink. Thus, current scheduling techniques such as those above have not fully addressed QoS differentiation features that are becoming necessary for wireless data network operators to differentiate their services offerings from those of their competitors, in an effort to generate additional revenue. Accordingly, differences in performance for users in different service classes currently may not be perceivable by the end user, thus network operators need to see a benefit to a QoS feature, such as a QoS differentiation feature, before they purchase system equipment implementing such features.